Decohered Pairs Yield Entangled Photons

Scientists at the Graduate University for Advanced Studies, Japan Science and Technology Corp. NTT Basic Research Laboratories in Japan have demonstrated that polarization-entangled photons suitable for applications such as quantum cryptography can be produced using two decohered photon pairs. They presented the results of their experiments in the Jan. 23 issue of Nature.

The setup incorporated half-wave plates, polarizing beamsplitters and a liquid crystal retarder to induce identical phase fluctuations on two pairs of photons generated by spontaneous parametric down-conversion in BBO crystals. By sharing the results of their measurements on two modes classically, the communicating parties can extract a pair of entangled photons with a fidelity of between 0.78 and 0.89.